Problems with aliases and searches
Colin Robbins <c.robbins@xtel.co.uk> Thu, 19 March 1992 11:39 UTC
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From: Colin Robbins <c.robbins@xtel.co.uk>
Message-ID: <"7328 Thu Mar 19 09:31:51 1992"@xtel.co.uk>
To: osi-ds@cs.ucl.ac.uk
Cc: g.lunt@xtel.co.uk, p.hennessy@xtel.co.uk
Subject: Problems with aliases and searches
Hello, I am not sure if this is the right list to send this to, please forgive me if it isn't (but were else are such thing discussed). Whilst developing a DUA we have come across a problem with searching subtrees and aliases. I include here, a message Graeme Lunt sent me describing the problem, then I'll try to expand a little! ---- Graeme's Message There is a distinct problem with aliases in the directory, especially when considering the user's perception of the model and the UA's ability to represent it. Consider the case where the user is browsing the directory - the normal mode of working will be to search aliases. A search will return a set of DNs which match but no indication of whether or not an alias was dereferenced. (Searches (singelevel) may be more commonly used in UA's than lists to allow the UA to restrict the view to a single object class). Now, when the user finds an entry they wish to delete, they will end up deleting the aliased object rather than the alias. (Because this is the DN they were returned in the search) Unless of course the UA is intelligent - a UA may guess that an alias has been de-referenced by comparing the prefix of the returned DNs with the position where the single level search took place. If they don't match, then it is likely an alias has been de-referenced. When the user selects a DN to delete (or modify), the UA can ask if the user means the alias or aliased object. If the user requests the alias, then the UA has to do some more work. It has to perform a search of the form objectClass=alias & aliasedObjectName=<aliasedObject> * If this search returns more than one result - the UA will have to go back to the user to determine which alias to edit - and the user may not know! However, there is still another problem. Above we said the UA could work out if an alias had been de-referenced by comparing prefixes. * This will not work if the alias references another object at the same position in the DIT - they have the same prefix ! The alternative of assuming the user knows best - they will switch on/off search aliases as required - does not work in practice. An example of this is when a user (with search aliases on) creates a new alias. A relisting at shows the new object (actually the de-referenced object), the user then decides the alias is wrong and deletes it - and in fact deletes the aliased object. This all becomes horribly complex when aliases can be de-referenced to arbitrary depth. ---- End Graeme's Message Here's an example... 1) c=GB @ o=X-Tel Servives Ltd @ cn=Colin Robbins 2) l=Europe @ o=Cosine @ ou=Paradise @ cn= Colin Robbins 3) l=Europe @ o=Cosine @ ou=Another Project @ cn= Colin Robbins 4) l=Europe @ o=Cosine @ ou=Paradise @ cn=David Goodman 5) l=Europe @ o=Cosine @ ou=Paradise @ cn=Project Manager Entries 2 & 3 are aliases pointing to entry 1). Entry 5 is an alias pointing to entry 4). [ Yes - I know according to the Barker/Kille Internet Draft Entry 5) is a bad use of alias, but such aliases may still exists in the DIT! ] Assume I am the manager of the o=Cosine branch of the DIT, and I want to do some modifications [maybe I have just read the Barker/Kille ID, and want to remove the bad alias!!!] I do a a subtree search below o=Cosine for "sn=Robbins" with the searchalias flag set. Entry 1) gets returned, with no indication that an alias has been dereferenced. (The alias dereference flag in the common result refers to aliases on route to the base object of the search, but not after). Also, I only get one resultant DN, even though there are 2 aliases. So as a user, I might blindly delete entry 1). I can't use subtree search o=Cosine with the "search aliases" flag off, because the search for "surname = robbins" would fail. So, I can't do a simple search. If I was able to guess the result was an alias, I could search the subtree for "objectclass = alias" and "aliasedobjectname = c=GB @ ... @ cn=Colin Robbins", and then decide which ones to delete - but that seems excessive,(and assume I know the real DN, but I guess I probably would by this stage). [I also understand that the '92 standards allow aliases to point at other aliases, which would mean this approach would not work.] The "guess" is possible in this case because of the DN prefix being different. But if I were to alter the search and look for "sn=Goodman", when it was the project manager alias I wanted to alter (but was not sure of the DN), the guess would not be possible because the DN prefixes are the same. Has anybody else come across this problem? I think what is needed is an indication in the X.500 search result of which alias has been dereferenced. Any other ideas? Should the Barker/Kille Naming guideline document flag this as a problem when discussing aliases? Colin PS Please cc: G.Lunt@xtel.co.uk in any responses as he is not on the osi-ds list.
- Problems with aliases and searches Colin Robbins
- Re: Problems with aliases and searches Colin Robbins
- Re: Problems with aliases and searches Steve Hardcastle-Kille
- Re: Problems with aliases and searches Steve Hardcastle-Kille
- Re: Problems with aliases and searches Colin Robbins
- Re: Problems with aliases and searches Steve Hardcastle-Kille